Amplifiers are electronic devices that typically increase the level of an electronic signal. Amplifiers have many characteristics that are often of concern to circuit designers. One such characteristic is the gain of the amplifier. The gain represents a quantification of the amount of amplification that is provided by the amplifier.
In many applications, it is important that the gain of the amplifier remain constant, notwithstanding variation in the temperature in which the amplifier operates, variation in the processes that are used to fabricate the components of the amplifier, and/or variation in the frequency of the signal that is delivered to the amplifier for amplification.
Variation in the temperature in which an amplifier operates often causes variation in the gain of the amplifier. This is because the temperature change often affects one or more operational parameters of one or more of the electrical components that are used in the amplifier. Changes in these operational parameters often cause corresponding changes in the gain.
Similarly, the operational parameters of one or more components in an amplifier are often affected by variation in the processes that are used to fabricate these components. Indeed, the operational parameters of an electronic component are often specified by their manufacturer to fall within a range, rather than having only a single value. The specification of such ranges explicitly reflects anticipated variation in fabrication process.
The frequency of the signal that the amplifier is given to amplify can also cause variation in the operational characteristics of one or more components in the amplifier. For example, the operational characteristics of transistors—devices commonly used in amplifiers—are often affected markedly by the frequency of the signal that is processed by the transistors. One typical cause of this variation is internal capacitance in the transistor, a characteristic that reacts differently to different frequencies.
There has been a need for amplifiers that have gains that remain substantially constant, notwithstanding significant changes in operating temperature, fabricating process or input frequency. Such a need is particularly present in the cellular communication art. In this art, operation at very high frequency is common and several amplifiers are often cascaded, effectively multiplying many of the problematic effects of gain instability.